This application claims the priority of the commonly owned copending German patent application Serial No. 101 06 416.0 filed Feb. 12, 2001. The disclosure of the aforementioned copending German priority application, as well as that of each US and foreign patent and patent application identified in the specification of the present application, is incorporated herein by reference.
The present invention relates to improvements in fluid operated systems, especially hydraulic systems, which employ cylinder and piston units. Examples of such units (also called hydraulic or pneumatic cylinders) are so-called slave cylinders and master cylinders which are utilized in the power trains of numerous motor vehicles, e.g., to engage and/or disengage a friction clutch between the prime mover (such as an internal combustion engine) and the change-speed transmission which latter selects the speed and the direction of movement of the vehicle.
As a rule, the piston of the master cylinder of the clutch actuating system in the power train of a motor vehicle is set up to furnish (when necessary or desired) a pressurized fluid to the housing (cylinder) of the slave cylinder by way of one or more conduits, and the piston in the cylinder or housing of the slave cylinder causes a lever, a fork or another suitable actuator or implement to engage or disengage the friction clutch so that the latter establishes or interrupts a torque transmitting connection between the rotary output element (such as a camshaft or a crankshaft) of the prime mover and the rotary input shaft of the transmission.
Published German patent application No. 44 05 581 discloses a master cylinder which employs a one-piece piston having a complex undercut portion for reception of an insert which defines a socket for one (spherical or dome-shaped) end portion of a piston rod. The piston is made of a plastic material by resorting to complex and hence expensive injection molding tools, or of a metallic material in a time-consuming operation by employing material removing implements.
The peripheral surface of the piston in a conventional master or slave cylinder cooperates with the internal surface of the housing to serve as a guide surface for the piston as well as to prevent leakage of hydraulic fluid from the chamber (such as a plenum chamber) of the cylinder. In the absence of a special treatment, the internal surface of the housing and/or the external surface of the piston undergoes pronounced wear after a relatively short period of use with attendant leakage as a result of the development of undesirable clearances and/or due to pronounced wear upon or total destruction of the seal or seals which is or are provided between the housing and the piston.
It is customary to provide a fluid reservoir or tank above or on top of the master cylinder (also called clutch cylinder). Such reservoir contains a supply of brake fluid or another suitable hydraulic fluid which is forced by the piston into the housing of the slave cylinder when the piston of the master cylinder is displaced in its housing in order to change the condition of the friction clutch. As a rule, the housing of the master cylinder is provided with a machined channel, groove or anoter suitable passage to establish a path for the flow of hydraulic fluid between the aforementioned fluid reservoir or tank and the chamber in the housing of the master cylinder when the piston is idle. The passage must be reliably sealed from the surrounding atmosphere during the entire useful life of the master cylinder which involves additional work and contributes to the cost of such hydraulic system.
A further drawback of presently known master cylinder-slave cylinder combinations is that they cannot compensate for the development of subatmospheric pressures in the housing of the master cylinder during retraction of its piston, i.e., such hydraulic systems are incapable of ensuring or of adequately ensuring satisfactory drawing of hydraulic fluid into the chamber which is defined by the housing of the master cylinder and its piston in order to prevent the development of cavitation while the piston is caused to return to its idle or starting position in which the pressure of fluid in the master cylinder assumes its lowest value.
An object of this invention is to provide a simple, inexpensive and long-lasting fluid-operated system, especially a hydraulic system, which employs at least one cylinder and piston unit and can be utilized with advantage in the power trains of motor vehicles as well as for numerous other purposes.
Another object of our invention is to provide a hydraulic system of the above outlined character which can be assembled and/or otherwise attended to by semiskilled persons.
A further object of the present invention is to provide a novel and improved method of making the piston and/or the housing of the cylinder and piston unit for use in a hydraulic system which is or which can be employed in a power train, e.g., to actuate the friction clutch and/or the brake(s) in the power train of an automobile or another motor vehicle.
An additional object of the instant invention is to provide novel and improved articulate connections between the pistons and piston rods in the cylinder and piston units which can serve as master cylinders or slave cylinders in the power trains of motor vehicles, such as passenger cars, trucks, suburban vehicles and many others.
Still another object of this invention is to provide a master cylinder or a slave cylinder which employs or which can operate properly by employing fewer sealing rings, sealing lips and/or other types of sealing elements than heretofore known cylinders.
A further object of our invention is to provide a master cylinder or a slave cylinder which can reliably draw oil or another hydraulic fluid into the chamber of its housing during each retraction of the piston to or toward its starting position.
Another object of the present invention is to provide a novel and improved method of articulately anchoring the piston rod in the socket of the piston or another part of a hydraulic cylinder and piston unit, for example, in the power train of a motor vehicle.
An additional object of the invention is to provide novel and improved means for mounting one or more seals in the housing of a hydraulic cylinder and piston unit of the above outlined character.
Still another object of the instant invention is to provide a novel and improved piston for use in a hydraulic cylinder and piston unit.
A further object of the invention is to provide a novel and improved housing or cylinder for use in a hydraulic cylinder and piston unit, particularly in the power train of a passenger car or another combustion engine-driven or otherwise power-driven conveyance.
Another object of the invention is to provide a novel and improved method of reducing the extent of wear upon and of prolonging the useful life of the piston and/or housing and/or sealing means and/or other constituents of hydraulic cylinder and piston units.
An additional object of the invention is to provide a novel and improved method of constructing, configurating and assembling the constituents of a master cylinder or a slave cylinder in such a way that they are automatically locked to each other as soon as they are properly positioned relative to one another.
Still another object of our invention is to construct the constituents of a master cylinder, a slave cylinder or another fluid-operated or fluid conveying and/or compressing cylinder and piston unit in such a way that they are automatically limited or confined to requisite (permissible) movements with and/or relative to each other as soon as their assembly with one another and/or with one or more additional constituents is completed.
An additional object of our instant invention is to provide a power train, particularly for use in motor vehicles, which embodies one or more master cylinders and/or slave cylinders with pistons, piston rods, seals and other constituents of the above outlined character.
A further object of this invention is to prolong the useful lives of cylinder and piston units in a simple and inexpensive manner, by resorting to available equipment and by employing readily available and relatively inexpensive materials.
One of several features of the present invention resides in the provision of a hydraulic system which comprises a first cylinder and piston unit including a first fluid-containing housing and a first piston which is reciprocable in such housing, and a second cylinder and piston unit including a second fluid-containing housing and a second piston which is reciprocable in the second housing. At least one of the pistons consists at least in part of a thermosetting material, and the improved hydraulic system further comprises at least one fluid-conveying conduit which connects the first housing with the second housing.
The first unit can constitute the master cylinder and the second unit can constitute the slave cylinder of a power train in a motor vehicle wherein the slave cylinder serves to actuate a clutch, such as a friction clutch. Such hydraulic system can further comprise means for varying the pressure of hydraulic fluid in the first housing by way of the first piston; the pressure varying means can comprise a clutch pedal and a piston rod which articulately connects the pedal with the first piston, preferably by way of a novel ball and socket joint.
The at least one piston can constitute a shaped article, e.g., a product which is turned out in accordance with a pressing, an injection pressing, an injection molding or an analogous technique.
Suitable thermosetting materials for the making of the at least one piston include melamine, phenolic resins, epoxy resins, unsaturated polyesters, silicon resins, urea and formaldehyde.
The at least one piston can be reinforced, for example, by glass fibers.
An external surface of the at least one piston can be guided by an internal surface of the respective housing, and the hydraulic system can further comprise at least one sealing element, such as a ring-shaped seal, which is in sealing engagement with the surface of the at least one piston.
The at least one piston and the respective housing define a variable-volume chamber for hydraulic fluid, and such system further comprises at least one seal which is interposed between the at least one piston and the respective housing. Such housing preferably includes a one-piece section which cooperates with the at least one piston to define the variable-volume chamber.
Another feature of the present invention resides in the provision of a variable-condition hydraulic system which comprises a master cylinder including a first housing and a first piston which is reciprocable in and defines with a section of such housing a first fluid-containing chamber, a slave cylinder including a second housing and a second piston which is reciprocable in and defines with the second housing a second fluid-containing chamber, at least one hydraulic connection between the two chambers (such connection can include two conduits and a throttle valve between them), a source of hydraulic fluid (e.g., brake fluid), at least one conduit which serves to connect the source with the first chamber, and a seal which is interposed between the first piston and the section of the first housing. The seal is movable within limits relative to the first piston between a plurality of positions in dependency upon the condition of the hydraulic system.
The seal is or can be arranged to establish communication between the at least one conduit and the first chamber in at least one predetermined position of the seal relative to the first piston. Such seal can be arranged to move to the at least one predetermined position as a result of frictional engagement with the first piston, and the first piston is movable relative to the section of the first housing through a predetermined distance from an end position; the at least one seal is or can be arranged to share a predetermined stage of movement of the first piston.
The arrangement can be such that the seal is movable relative to the first piston in response to changes of fluid pressure in the first chamber.
The seal can be arranged to establish with the first piston and/or with the first housing at least one path for the flow of fluid between the at least one conduit and the first chamber in at least one of the aforementioned plurality of positions of the seal relative to the first piston.
The seal has a first surface which is in at least temporary sealing engagement with an end face of the first piston, and a second surface which is in at least temporary sealing engagement with an internal surface of the first housing. The first surface of the seal can be provided with at least one annular projection or bead which is movable into and from sealing engagement with the end face of the first piston.
The improved hydraulic system can further comprise a control ring which is movably interposed between the first piston and the first housing; the seal in such system can include a first annular projection (e.g., a bead) which serves to sealingly engage an annular end face of the first piston, and a second annular projection (e.g., a second bead) which surrounds the first annular projection and serves to sealingly engage an end face of the control ring.
The first piston is or can be reciprocable in the section of the first housing to increase and reduce the pressure of fluid in the first chamber, and the seal can be arranged to seal the first chamber from the at least one conduit in response to an increase of fluid pressure in the first chamber. Such seal can be further arranged to intensify the sealing action between the at least one conduit and the first chamber in response to increasing fluid pressure in the first chamber. This seal can be installed for movement relative to the first piston in response to movement of the first piston in a direction to reduce the fluid pressure in the first chamber.
The first piston can be provided with an axial extension (such as a tubular extension), and the seal can constitute a ring which is axially movably mounted on the extension. Such master cylinder can further include a carriage (such as a sleeve-like part) which is surrounded by and is arranged to share the movements of the seal. The carriage can be installed to axially movably surrond the extension of the first piston. Such extension can be provided with a radially outwardly extending stop which serves to limit the extent of movability of the carriage relative to the first piston. The carriage can be mounted on the extension of the first piston as a result of movement over the stop of the extension, and the stop can be provided with a substantially conical surface or slope which serves to facilitate rapid and convenient mounting of the carriage on the extension. To this end, the tubular extension can be provided with at least one elongated slot to permit radial contraction during mounting of the carriage on the extension. In addition to or in lieu of such slot in the extension, the tubular carriage can be provided with a slot which is arranged to permit radial expansion of the carriage during mounting on the extension.
An open end of the at least one conduit can serve as an inlet or as an outlet for hydraulic fluid and is located at the aforementioned section of the first housing. The seal can be arranged to directly seal the open end of the at least one conduit in at least one of the aforementioned plurality of its positions.
Still further, the hydraulic system can be operated in such a way that the first piston (i.e., the piston of the master cylinder) is movable relative to the aforementioned section of the first housing to an idle position in which the source of hydraulic fluid communicates with the first chamber by way of the at least one conduit. The section of the first housing can be provided with at least one channel which establishes at least a portion of a path for the flow of fluid between the at least one conduit and the first chamber in an end position of the seal and while the first piston is idle. The at least one channel can include at least one groove provided in an internal surface of the aforementioned section of the first housing. Such hydraulic system can further include a control ring which is axially movably interposed between the first piston and the first housing and has at least one opening defining a second portion of the path in a predetermined axial position of the control ring relative to the aforementioned section of the first housing. Such hydraulic system can further comprise a stop which is provided in the first housing and serves to arrest the control ring in the predetermined axial position relative to the section of the first housing.
The seal can be arranged to normally seal the at least one conduit from the first chamber and to establish a path for the flow of fluid between the at least one conduit and the first chamber in response to movement to at least one of a plurality of positions. The seal is movable, at least in part, by the first piston and assumes the at least one position in response to assumption by the first piston of an end position relative to the first housing.
At least a portion of the at least one piston can consist, at least in part, of a thermosetting plastic material.
The hydraulic system further comprises means (such as a pivotable pedal and a piston rod) for reciprocating one of the pistons relative to the respective housing, and such reciprocating means can include a ball and socket joint.
A further feature of the present invention resides in the provision of a ball and socket joint, e.g., to move the piston of the master cylinder in the power train of a motor vehicle relative to the housing of such master cylinder. The improved ball and socket joint comprises a reciprocable piston, a connector provided on the piston and having a socket, a piston rod having an at least substantially spherical head received in the socket with freedom of swivelling movement, and means for securing the connector to the piston. In accordance with a feature of the invention, the spherical head is disposed between an elongated portion (such as a shank) of the piston rod and the securing means.
The piston can be provided with a stepped axial hole and the connector can include a portion extending into such hole. The securing means of such joint can include means for anchoring the aforementioned portion of the connector in the hole. Such portion of the connector can include a plug and the anchoring means can include a form-locking connection between the plug and the piston; such form-locking connection can include one or more snap fasteners. Alternatively, the anchoring means can include a force-locking connection between the plug and the piston, and such force-locking connection can include the establishment of a force fit between the plug and the piston.
The securing means can include mating threads on the plug of the connector and in the piston.
It is also possible to employ securing means which consists of or includes an undercut provided on the connector or on the piston rod and a complementary part provided on the piston rod or connector and received in the undercut. The connector can be slotted in the region of the undercut. Alternatively, the connector can include a radially expandible elastic portion which is disposed in the region of the undercut and is non-expandibly surrounded by the piston or by the housing or cylinder for the piston.
The connector can include an annular array of radially outwardly expandible segments which surround the socket, and a ring-shaped retainer which surrounds the segments. Such connector can be a separately produced part or it can be of one piece with the piston.
If the connector is part of the piston, the securing means can include an undercut provided on the piston or on the piston rod and a complementary part which is received in the undercut and is provided on the piston rod or on the piston. The complementary part can include one or more protuberances which are or which can be provided on the piston. At least a portion of such piston can consist of a thermosetting material.
Still another feature of the present invention resides in the provision of a ball and socket joint which comprises a piston including an end portion having a concave socket, a piston rod having a spherical head in the socket, and a connector including a cover overlying the end portion of the piston, surrounding the piston rod adjacent the head, and being affixed to the piston. The cover can include a radially extending substantially wedge-shaped recess and a central opening receiving the piston rod adjacent the head and communicating with the recess. The opening is or can be at least substantially round and the narrowest portion of the radial recess preferably exhibits a width which is less than the diameter of the central opening. At least a portion of the piston can consist of a thermosetting material, e.g., of one of the afore-enumerated thermosetting materials.
An additional feature of our present invention resides in the provision of a cylinder and piston unit, such as the master cylinder or the slave cylinder in the power train of a motor vehicle. Such cylinders can be utilized to actuate the brake(s) or to actuate (such as disengage) the friction clutch between the prime mover and the change-speed transmission of the motor vehicle. The improved cylinder and piston unit comprises a housing (e.g., a housing including two sections which are sealingly fitted into each other), and a piston in the housing. The housing is reciprocable relative to the piston and/or vice versa and the housing and/or the piston can be made, at least in part, of a thermosetting plastic material. Such cylinder and piston unit normally further comprises one or more seals (such as annular seal or seals) which is or are sealingly interposed between the housing and the piston. The seal or seals can perform several tasks, such as sealing the internal chamber of the housing from the surrounding atmosphere as well as of regulating the flow of hydraulic fluid between one or more sources and the internal chamber or chambers of the housing.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved hydraulic system itself, however, both as to its construction and the modes of assembling and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.